It has been proposed that heat-shrinkable elastics be used in the formation of disposable garments. such heatshrinkable elastics are known to find particular use in the formation of waist bands for disposable diapers for incontinent garments. The formation of diaper garments with heat-shrinkable elastic at the waist is illustrated in the method and apparatus of UK patent application No. GB 1,136,678--Chapman et al. In the method and apparatus illustrated there the elastic is placed cross-direction to the movement of the web that forms the backing of the diaper. Subsequent treatment of the discrete articles with heated air at about 68 degrees C. is disclosed as suitable to cause the elastically-contractible elements to shrink.
It is also disclosed in copending U.S. patent application U.S. Ser. No. 605,968, filed May 1, 1984, W. S. Pomplun et al., "Formation of Elasticized Portions of Disposable Garments and Other Articles." The copending application, coassigned with the instant application, discloses a method and apparatus for heating a heatshrinkable elastomer. The heating method and apparatus utilizes heated air at about 175 degrees F.
It has been proposed in copending application entitled "Method and Apparatus for Activating Heat-shrinkable Ribbon on Disposable Garments and Other Articles," Roland et al., Ser. No. 718,410 filed Apr. 1, 1985, that the method and apparatus for activating the heat-shrinkable material be a source of radiant energy with air flow conditionally contributing to heating of the materials.
While the above methods are believed to be successful, there remain problems with the processes and apparatus. The process of diaper formation is performed at very high speed. During high speed processing all diapers may not be folded in exactly the same manner so that the heat-shrinkable waist materials may be somewhat hidden and not susceptible to good heat transfer by air or direct exposure to the radiant energy. Further, there is a difficulty in that the polymer backing material for a diaper is formed of a low-melting polymer such as polypropylene that will melt if it it heated significantly. The difficulty with prior systems is that at high speeds the elastic may not be adequately exposed to either radiant energy or heated air to cause complete shrinking of the heat shrinkable elastic. Therefore, there remains a need for an improved high-speed system for shrinkage, particularly for the elastic at diaper waist.